But the game most gamers want Valve to release remains illusive. That game being Half-Life 3. However, the launch of Source Filmmaker has brought to light a major reason Half-Life 3 may not have appeared yet: it could be the first game Valve releases using a brand new game engine.

Since 2004 Valve has been using and developing its Source engine. It’s the game engine that powers everything from Counter-Strike: Source through Half-Life 2, both Portal games and both Left 4 Dead titles. But eventually the tech needs a major overhaul from the ground up, and there’s now plenty of evidence a new engine, called Source 2, is actively being developed.

Searching through the files supplied with Source Filmmaker has revealed 60+ references to “Source 2″ as a target. It seems Valve is trying to keep the same asset pipeline in place, but allowing content to target either engine. By doing so it should allow an easy transition to the new engine for existing developers, modders, the tools they use, and possibly even existing Source games.

As well as references to the names, a bunch of icons thought to be for Source 2 tools have been discovered:

A new engine means Valve can better take advantage of existing hardware features, be that PC graphics cards or consoles. It also means new games, like Half-Life 3 will have that next-gen sheen and should be able to simultaneously release across multiple platforms (Windows, Linux, Mac, PS3, Xbox 360, and whatever hardware appears in the near future).

Valve has yet to officially comment, but with the Source engine now in its 8th year, I don’t think many people would be surprised to see it replaced soon. And I’m sure we all hope the Source 2 launch game has a “3” at the end of the title.